1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine that serves to temporarily store evaporated fuel generated in a fuel tank or the like into a canister (evaporated fuel adsorption device), and introduce it into an intake system of the internal combustion engine as purge air together with air. Also, the invention relates to a control apparatus for an internal combustion engine that serves to introduce evaporated fuel that leaked from a gap between a cylinder and a piston received therein of the internal combustion engine into an intake system thereof as a blowby gas together with air. More specifically, the invention relates to a control apparatus for an internal combustion engine capable of achieving excellent air fuel ratio control even in case a large amount of evaporated fuel is processed or treated.
2. Description of the Related Art
In the past, there has been known an evaporated fuel treatment device in which evaporated fuel generated in a fuel supply system such as a fuel tank of an internal combustion engine, after being adsorbed to and stored in a canister, is mixed with air and introduced into an intake system thereby to purify (or purge) the canister (see, for example, a first patent document: Japanese patent No. 3511722).
In addition, it is also generally known that when the evaporated fuel adsorbed to the canister is introduced into the intake system together with air, there will occur a deviation between an actual air fuel ratio and a target air fuel ratio that is a target to be controlled in accordance with the concentration of the evaporated fuel in the purge air.
Accordingly, in the conventional apparatus as described in the above-mentioned first patent document, the actual air fuel ratio is brought close to the target air fuel ratio by correcting the amount of fuel to be injected according to air fuel ratio feedback control. Specifically, provision is made for a means for calculating the concentration of purge air in an intake air from a purge rate and a corrected amount of fuel according to the air fuel ratio feedback control, and correcting the amount of fuel to be injected in accordance with the purge rate and the purge air concentration.
Here, note that purge air is introduced into a surge tank from a purge passage (generally connected to an upstream side of the surge tank), and air sucked through an air flow sensor is introduced into the surge tank through a throttle valve.
Moreover, the fuel injected from an injector is introduced into an intake port and/or a combustion chamber, and an air fuel ratio sensor for detecting the air fuel ratio is arranged in an exhaust passage (generally, a collected portion of the exhaust passage in which exhaust gases from respective cylinders are collected together).
On the other hand, there has also been proposed an apparatus with an actual purge rate estimation section that estimates, in consideration of the occurrence of a transport delay of air in the intake system of the internal combustion engine, a purge rate (actual purge rate) in a mixture actually sucked into a combustion chamber of the internal combustion engine based on the conductive state of the purge passage before a predetermined period of time (see, for example, a second patent document: Japanese patent No. 3409891).
In the conventional apparatus described in the second patent document, the conductive state of the purge passage is stored at each sampling time interval, and a delay time is decided in accordance with the operating condition of the internal combustion engine, whereby an amount of purge flow contained in the intake air to be sucked into the internal combustion engine is accurately estimated while further applying gradually changing processing (filtering processing) thereto in accordance with the operating condition of the internal combustion engine.
In addition, there has been proposed an apparatus including a purge detection delay calculation section for calculating a purge detection delay time from a time point at which purge air is introduced into an intake system until a time point at which the purge air thus introduced is actually detected as an air fuel ratio by means of an air fuel ratio sensor installed on an exhaust system (see, for example, a third patent document: Japanese patent No. 3376172).
The purge detection delay calculation section described in the above-mentioned third patent document calculates the purge detection delay time based on an intake air transport delay time from the air flow sensor to the intake system, a correction time due to the charging efficiency of the intake system, the length of an exhaust passage from a combustion chamber to the air fuel ratio sensor, and a response delay time of the air fuel ratio sensor.
In the above-mentioned conventional control apparatus for an internal combustion engine, attention is primarily focused on the transport delay of purge air alone, but in actuality, purge air is introduced from a purge passage into a surge tank, into which intake air is also introduced through a throttle valve, and fuel injected from an injector is led into an intake port (or combustion chamber), with the air fuel ratio sensor being installed on the exhaust passage. As a result, it is necessary to correct the amount of fuel to be injected by calculating the concentration of purge air from the air fuel ratio detected by the air fuel ratio sensor while taking into consideration all the transport delays of the purge flow rate (the flow rate of purge air), the amount of intake air and the amount of fuel which are used for controlling the air fuel ratio.
According to the above control that considers only the transport delay of purge air, as in the above-mentioned conventional apparatuses, there arises the following problem. That is, particularly, in case where the amount of purge air introduced changes greatly great, or where the amount of intake air changes greatly, there occurs a deviation in phase of the purge flow rate, the amount of intake air, and the amount of correction for the amount of fuel injected by the injector, so the air fuel ratio cannot be maintained to a target air fuel ratio (e.g., stoichiometric air fuel ratio), and, as a result, the exhaust gas is deteriorated.
Also, there are the following additional problems in the above-mentioned conventional apparatuses. Since the amount of data required to be set is large, resultant calibration man-hours increase, and besides, the memory capacity used in a digital computer of a controller becomes large, thus inviting an increase in size and cost.
For example, in the conventional apparatus as described in the above-mentioned second patent document, a memory means is required for storing the conductive state of the purge passage at each sampling time interval, so the memory capacity required becomes large, and in order to decide the delay times in accordance with the operating condition of the internal combustion engine, or in order to perform gradually changing processing in accordance with the operating condition of the internal combustion engine, calibration man-hours required accordingly increase.
In addition, in the conventional apparatus as described in the above-mentioned third patent document, the settings of the intake air transport delay time, the correction time due to the charging efficiency, and the response delay time of the air fuel ratio sensor are needed, so the amount of data for which settings are necessary increases, thus resulting in accordingly increased calibration man-hours.